1. Field of the Invention
The present invention relates to a hybrid drive system for hybrid powered vehicles equipped with an oil-operated transmission.
2. Description of Related Art
Generally, vehicles are equipped with an oil pump that forces an operating oil to specific oil-operated devices such as a transmission and oil-lubricated devices such as rotating parts and sliding parts. In ordinary engine driven vehicles, this oil pump is commonly driven by an engine. In this regard, hybrid powered vehicles that are equipped with an internal combustion engine and an electric traction motor commonly use an extra driving device for the necessity of driving the oil pump even during a halt of the engine. There is disclosed in, for example, Japanese Unexamined Patent Publication No. 11-98601 one of approaches to the hybrid drive system in which an extra driving device is used to cause stable operation of auxiliary devices such as the oil pump installed in such a hybrid powered vehicle irrespective of engine operating conditions. The solution is to exclusively use an electric motor to drive auxiliary devices including an air compressor, a compressor of air conditioning system, an oil pump for a power steering system and the like, separately apart from the engine.
Incidentally, it is conceivable to use an electric motor for exclusively driving an oil pump that forces an operating oil to oil-operated devices such as a transmission and oil-lubricated parts of the hybrid powered vehicle on the basis of the teaching of the above mentioned publication.
In that case, the hybrid powered vehicle has to be equipped with an extra electric motor. This causes a cost increase of the hybrid powered vehicle. Further, this cause an increase in battery power consumption.
It is therefore an object of the present invention to provide a hybrid drive system for a hybrid powered vehicle that can always drive an oil pump with less battery power consumption irrespective of engine operating conditions and is fabricated at low costs.
The foregoing object of the present invention is accomplished by a hybrid drive system for a hybrid powered vehicle equipped with a transmission, which comprises an internal combustion engine operationally connected to the transmission through a first clutch, a battery-operated traction motor operationally connected to the transmission, a battery-operated auxiliary motor, as an engine starter, operationally connected to the engine through a second clutch, and an oil pump operative to force an operating oil to specified oil-operated and/or oil-lubricated devices and parts including at least the transmission. The oil pump is operationally connected to the auxiliary motor before the second clutch so as to be driven by the auxiliary motor whenever the auxiliary motor is driven.
The hybrid drive system that is provided with the oil pump driven by the starting motor has no necessity of having an extra motor exclusive to the oil pump.
According to the arrangement of the hybrid drive system in which the oil pump is dispose between the starting motor and the second clutch, the oil pump is always driven by the starting motor irrespective of whether the second clutch has been engaged to drive the engine for a start by the auxiliary motor or the second clutch has been disengaged after a start of the engine or a halt of the engine. Therefore, the hybrid drive system of the present invention securely forces an operating oil to the oil-operated and/or oil-lubricated devices and parts including the transmission irrespective of the states of engine.
The hybrid drive system may further comprises alteration means for operationally connecting the oil pump to the traction motor and the starting motor. That is, the alteration means operates to selectively connect the oil pump to the traction motor when an input speed of rotation to the alteration means from the traction motor is higher than an input speed of rotation to the alternation means from the starting motor and to the starting motor when an input speed of rotation to the alteration means from the traction motor is lower than an input speed of rotation to the alteration means from the starting motor. Accordingly, even while the traction motor operates in a range of lower speeds of rotation, the oil pump is driven by the auxiliary motor, so as to force a necessary amount of an operating oil to the specified devices and parts including the transmission. In addition, the hybrid drive system makes it possible to stop the starting motor while the oil pump is driven by the traction motor with an effect of stopping supply of battery power to the starting motor. This is desirable to save battery power consumption.
The alteration means comprises a first one-way clutch that disposed between the traction motor and the oil pump so as to operationally connect the oil pump to the traction motor during normal rotation of the traction motor and operationally disconnect the oil pump from the traction motor during reverse rotation of the traction motor, and a second one-way clutch disposed between the auxiliary motor and the oil pump so as to operationally connect the oil pump to the auxiliary motor during normal rotation of the auxiliary motor and operationally disconnect the oil pump from the auxiliary motor during reverse rotation of the auxiliary motor.
The hybrid drive system may further comprises an additional oil pump connected to the traction motor before the first clutch. The oil pump operationally connected to the auxiliary motor is of a high pressure-low discharge type and the additional oil pump connected to the traction motor is of a low pressure-high discharge type.
According to the hybrid drive system, even in a region where the amount of operating oil discharged by the additional oil pump driven by the traction motor is insufficient with respect to the necessary amount of operating oil for the specified oil-operated and/or oil-lubricated devices and parts including at least the transmission due, for example, to a low speed of rotation of the traction motor, the oil pump can be driven by the auxiliary motor to make up for the insufficiency. As a result, the specified oil-operated and/or oil-lubricated devices and parts are always securely provided with the necessary amount of operating oil. While, on one hand, it is common to provide the oil-operated devices such as the transmission with high pressurized operating oil at a low rate, it is also common to provide the oil-lubricated devices and parts with low pressurized operating oil at a high rate. If using a single oil pump in order to provide an necessary amount of operating oil covering all of the oil-operated and oil-lubricated devices and parts, it is essential for the oil pump to have a large capacity of discharging and pressurizing. Such the large capacity oil pump causes a large pump loss. However, according to the hybrid drive system, each of the high pressure-low discharge type oil pump and the low pressure-high discharge additional oil pump has its own region that forms a part of the entire region of operating oil supply. This realizes an oil pump system optimized in operation with respect to the necessary amount of operating oil and having less pump loses.
According to the hybrid drive system, when the vehicle is driven back, the traction motor rotates in the reverse direction. However, since the first one-way operationally clutch disconnects the oil pump from the traction motor, the oil pump does not rotate in the reverse direction. Further, at this that time, since the second one-way clutch operationally connects the oil pump to the auxiliary motor rotating in the normal direction, so that the oil pump is driven by the auxiliary motor even when the vehicle is driven back to force an operating oil to the transmission.
The hybrid drive system according to another embodiment of the present invention comprises an internal combustion engine operationally connected to the oil-operated transmission through a first clutch, a battery-operated traction motor operationally connected to the oil-operated transmission so that it is driven ordinary by a battery and can be driven by the engine to charge the battery while the traction motor is disconnected from the battery, a battery-operated auxiliary motor operationally connected to the engine through a second clutch so as to start the engine and can be driven by the engine to charge the battery while the auxiliary motor is disconnected from the battery, and an oil pump operationally connected to the traction motor so as to force an operating oil to the oil-operated transmission.
According to the hybrid drive system, the oil pump is driven directly by the traction motor that is driven by the engine while the vehicle is traveling with the aid of the engine as well as while the vehicle is traveling with the aid of the traction motor. In consequence, the oil pump is always driven to securely force an operating oil to the specified oil-operated and/or oil-lubricated devices and parts including the transmission. While the vehicle is traveling with the aid of the engine, the traction motor can be disconnected from the battery.